(a) Field of the Invention
The present invention relates to a link adaptation method using feedback information for a wireless communication system. More particularly, the invention relates to a link adaptation method using feedback information for a wireless communication system, which transmits and receives data depending on the state of a data transmission link to increase transmission capacity.
(b) Description of the Related Art
Link adaptation in a data communication system is a technique that selects a transmission power, a modulation method, a packet length, etc. depending on the state of a link through which data is transmitted and received so as to increase the transmission capacity of the data communication system. The link adaptation technique is divided into a technique of supposing symmetry of a link, and a technique of supposing asymmetry of a link. The former considers the state of a data transmission link from an access point (AP) to a station (STA) to be identical to that of a transmission link from the STA to the AP, while the latter supposes that the state of the data transmission link from the AP to the STA is different from the state of the data transmission link from the STA to the AP.
FIG. 1 shows a forward link and a backward link of a wireless communication system including an AP 110 and a STA 120. Referring to FIG. 1, a data transmission link from the AP 110 to the STA 120 is called a forward link and a data transmission link from the STA 120 to the AP 110 is called a backward link, in general.
When the two links are asymmetrical, a level of interference at a receiving side is varied with the position of the receiving side and it is different from a level of interference at a transmitting side. Thus, a transmission power and a modulation method for data transmission of the transmitting side should be decided at least partially from the standpoint of the receiving side.
For this, the STA monitors a channel state of the forward link to propose a transmission modulation method suitable for the AP when the STA communicates with the AP. Furthermore, link adaptation through a feedback method is required when backward data needed to decide the modulation method is transmitted.
A conventional data transmission and reception technique depending on a wireless link state is disclosed in U.S. Pat. No. 6,567,375, entitled “Method and Apparatus for Packet Size Dependent Link Adaptation for Wireless Packet”, which proposed a technique that changes a packet length and a coding method depending on a wireless link state to reduce data transmission delay time. However, this technique did not consider various parameters in a wireless communication system other than the packet length and coding method, and proposed only a method of shortening the data transmission delay time. Furthermore, it cannot solve problems with respect to system transmission capacity and power consumption of stations.